O. Babushkin

Yttria-alumina-silica glasses with addition of zirconia

Abstract ZrO 2 -free glasses and glasses containing ZrO 2 in the system Y 2 O 3 -Al 2 O 3 -SiO 2 have been investigated. Properties of compositions fired in nitrogen at 1600, 1650 and 1700 °C have been assessed. The solubility limit of ZrO 2 in yttrium aluminosilicate liquids with a high content of Y 2 O 3 at 1700 °C was determined to be 6 wt%. The hardness and density of the ZrO 2 -containing glasses were slightly increased compared to the ZrO 2 -free glass; y - Y 2 Si 2 O 7 (at temperatures 2 Si 2 O 7 (at temperatures >1300 °C) monoclinic phases are the main products formed during the crystallization. An unidentified intermediate phase rich in Y, Al and Si was observed to undergo a transformation at temperatures ≥1200 °C resulting in the formation of the β-Y 2 Si 2 O 7 phase.

Zirconia as a nucleating agent in a yttria-alumina-silica glass

Abstract The crystallization behaviour of a ZrO2-containing glass and a ZrO2-free glass in the Y2O3-Al2O3-SiO2 system prepared at 1700 °C were compared in order to study the influence of ZrO2 on the nucleation and growth processes. Techniques used included SEM, DTA and XRD analysis. The microstructural development of the ZrO2-containing material during crystallization was more complex than that of the ZrO2-free material. In the crystallization treatments no phase separation prior to crystallization could be observed and no precursor crystalline phase was observed to form in the ZrO2-containing glass. Thus the added zirconia could be considered to act as a growth modifier rather than a catalyst nucleating agent.

Reaction sequence in the formation of perovskite Pb(Zro0.48Ti0.52)O3—Pb(Nb23Ni13)O3 solid solution: Dynamic heat-treatment

Abstract The sequence of the solid state reactions in the PbOZrO 2-TiO2-Nb2O5-NiO system has been investigated. The oxide mixing route utilised in sample preparation was selected in order to determine the basic reaction path in the formation of the PZTPNN perovskite phase. It has been established that the main intermediate phases formed prior to PZTPNN are PbTiO3 and pyrochlore Pb-Nb-based phases. The sequence in the pyrochlore formation was from tetragonal Pb3Nb2O8 (500 °C) to rhombohedral Pb2Nb2O7 (600–750 °C) and finally to cubic Pb3Nb4O13 (650–850 °C). The formation of the perovskite phase proceeded from mutual solubility of PbTiO3 and pyrochlore Pb3Nb4O13 phases, accompanied by dissolving of residuals (PbZrO3 and NiO) in the perovskite solid solution formed.

Mechanical-thermal synthesis of Al2O3-Cr composite powders

Three different approaches have been investigated to synthesize alumina-chromium composites by displacement reactions between aluminium and chromia. The reactions have been performed either by pure ...

PZT phase formation monitored by high-temperature X-ray diffractometry

The crystallisation kinetics of amorphous sol-gel PZT thin films were investigated using high-temperature X-ray diffraction. Crystallisation for different isotherms was monitored as a function of time. Phase transformation data were obtained from integrated X-ray peak intensities which were calibrated based on image analysis of the surface microstructure of the samples at the end of the isothermal treatments. An activation energy of 310 kJ/mol was obtained without assuming a specific kinetic model. From the transformation data, a TTT diagram was constructed for the ranges studied.

Thermal expansion of hot isostatically pressed hydroxyapatite

A dense and transparent hydroxyapatite produced by hot isostatic pressing was investigated with respect to its stability and thermal expansion behaviour in the range 20–1150 °C. The evaluation was made by high-temperature X-ray diffraction in a reconstructed test chamber with a BN sample holder and Pt as an internal (in situ) reference. No degradation of the hydroxyapatite was detected in the range investigated. The lattice parameters, aand c, were determined as a function of temperature. The linear thermal expansion coefficient, determined by dilatometry, was 17.1 × 10–6°C–1, which agreed well with the value 17.3 × 10–6°C–1 obtained by X-ray diffraction.

Nitridation study of reaction-bonded silicon nitride in situ by high temperature X-ray diffraction

Abstract The reaction-bonded silicon nitride (RBSN) nitriding process has been studied using a high temperature X-ray diffractometer (HT-XRD) under isothermal conditions in the temperature interval 1300–1400 °C. With HT-XRD, the nitridation reaction and phases formed could be monitored almost instantaneously at temperature. The experimentally observed kinetics of the nitriding reaction were found to be in fair agreement with a theoretical model which predicts that the nitriding reaction occurs predominantly by Knudsen diffusion of nitrogen molecules through channels in a layer of growing Si 3 N 4 . However, no single rate law is likely to describe the whole nitridation process. Observation of the microstructure after nitridation indicates that the process occurs partly by reaction of Si vapour with nitrogen gas but that inward diffusion of nitrogen into particles also contributes significantly to the overall nitridation. The phase analysis showed that α-Si 3 N 4 formation predominates over β-Si 3 N 4 formation but the proportion of β-Si 3 N 4 increases as nitridation continues.

Kinetic Aspects of the Formation of Lead Zirconium Titanate

Abstract The kinetics of the second calcination step in the formation of PZT solid solution (with perovskite ABO 3 lattice) has been investigated by using two different particle sizes of the B-site precursor (1.91 and 5.08 μm), the finer size being obtained by prolonged milling. In-situ analysis performed by high-temperature X-ray diffractometry in a non-isothermal mode (20–800 °C) revealed a reduction of the calcination temperature by 100 °C with a decrease in particle size of the precursor. In order to clarify the mechanism of the solid-state reaction to PZT, isothermal heat treatment of the mixtures was performed in the temperature range 540–700 °C. The activation energies for the fine and the coarse powders were estimated as 150 and 210 kJ mol −1 respectively, and the reaction was found to follow the Jander model for diffusion-controlled solid-state reaction kinetics.

A high-temperature graphite furnace for X-ray powder diffraction

A modified computer-controlled high-temperature X-ray diffractometer with good stability and an upper temperature limit of more than 2300 K is described. a critical test of the system, determining the thermal expansion of Pt, Ni and AlN, showed close agreement with dilatometric and literature data. Lattice thermal expansion data of CrB2 and TiB2 up to 2100 K were also determined.

Crystallization of Y3Al5O12 from an oxynitride glass monitored by high-temperature X-ray diffractometry

Abstract It is well established that the glassy phase in a β-SiAlON material, with addition of Y 2 O 3 , can be crystallized to yttrium aluminium garnet (Y 3 Al 5 O 12 -YAG) by a post-sintering heat treatment. The crystallization of the YAG phase from an oxynitride glass with composition 46·1 wt% Y 2 O 3 , 26·3 wt% Al 2 O 3 , 21·6 wt% SiO 2 and wt% Si 3 N 4 was studied by means of high-temperature X-ray diffractometry. The kinetics of the crystallization were monitored in terms of the (420)) YAG peak area versus isothermal soaking time at 1150 °C during different heat treatments. The crystallization of the YAG phase was found to proceed as a surface crystallization. The results are relevant to developing improved crystallization treatments for glasses with potential for crystallization to YAG-based glass-ceramics and for heat treatments of YAG/β-SiAlON materials.